For instance, electric or electronic parts such as power transistor, driver integrated circuit (IC) or the like used in central processing units (CPU) or the like, act as heat sources, and recently said parts tend to be closely assembled, so that the amount of heat generated from said parts is increased, making heat radiation safeguards more important.
As heat radiation safeguards for said heat source, at present, the heat radiating member is used as a spacer between said heat source and a cooling part such as heat radiating housing or the like, so as to improve the thermal conductivity from said heat source to said cooling part. To improve the heat conduction efficiency from said heat source to said cooling part, said heat radiating member should be made of a material having good adhesion to both said heat source and said cooling part.
Up to now, a composite made of a resin material in to which a heat conductive filler has been added and dispersed so as to give heat conductivity to said resin material, has been provided.
As said resin material, mainly a silicone rubber has been used. Said silicone rubber can adhere to both said heat source and said cooling part.
Nevertheless, said silicone rubber has a problem in that said silicone rubber produces a low molecular weight siloxane, which causes a bad contact in the electric circuit. To solve said problem, a counter measure to suppress the production of low molecular weight siloxane has been promoted, but a sufficient measure has never been provided.
Further, since said silicone rubber is a cross-linked rubber, said silicone rubber has no thermoplasticity, so that recycling of said silicone rubber may be impossible.
On the one hand, said heat conductive filler has two types, one being an electroconductive filler, and the other, an insulating filler. It has been known that said electroconductive filler includes a metal group filler, such as copper filler, nickel filler, or the like, a carbon group filler such as graphite filler, or the like, and it has been known that said insulating filler includes a metallic oxide filler such as magnesium oxide filler, alumina filler, or the like, and silica, as the heat conductive filler used in said heat radiating member, especially said insulating filler has generally been used.
Further, since said electric or electronic parts are heat sources, high incombustibility may be required of said heat radiating member used therein from a safety viewpoint. To give said heat radiating member, high incombustibility, a flame retardant is added to the material of said heat radiating member. Said flame retardant has two groups, one being a halogen group, and the other a non-halogen group.
It has been known that the halogen group includes brominated flame retardant, chlorinated flame retardant, or the like, and the non-halogen group includes a non-halogen phosphorous flame retardant such as phosphate, or the like, and a metal hydroxide such as magnesium hydroxide, aluminum hydroxide or the like. Recently from the viewpoint that stresses on the environment should be reduced, the non-halogen group flame retardant may be mostly used.